The invention relates to a device and method for controlling propulsion in motor vehicles of the type generally disclosed in commonly assigned U.S. Pat. No. 4,794,539, which corresponds to German Published Unexamined Application (DOS) 3,545,715. In this patent, an arrangement is described in which a measurement value for the lateral vehicle acceleration, the yaw velocity or the speed difference between the front wheel speeds of rotation is compared with a mathematical value for this variable which is calculated from vehicle speed and steering angle, and if the values do not correspond, control signals are formed for the brakes of the wheels and/or for a power actuator of the vehicle engine. To obtain the most accurate possible values, adaptation electronics are provided which adjust the sensors needed for determining the input variables in the steady-state range of the roll steer characteristic of the vehicle so that identical speeds of rotation at all wheels and a steering angle of 0.degree. are measured in straight driving and so forth.
Since, however, the formula used and thus the mathematical value rarely corresponds precisely to the actual situations and thus to the mathematical value, a tolerance range around the mathematical value is there provided which can be varied with the vehicle speed and the steering angle and within which the measurement value should be located so that no intervention in the brakes or the vehicle engine is caused. The narrower this tolerances range can be kept the more effective the control system can operate.
However, the accuracy of the result of the calculation does not only depend on accurately adjusted sensors and a correct formula, it is also determined by other factors.
Due to inertia, the build-up of, for example, a lateral acceleration occurs as response to a change in steering angle with delay. The mathematical formula is designed for steady-state driving conditions and uses the new steering angle as a basis for calculating a value of lateral acceleration which actually only occurs with a certain delay. In addition, for example, lateral accelerations can also be measured in the case of straight driving with accurately adjusted sensors if driving occurs, for example, on a laterally inclined roadway or with non-uniformly distributed load.
Wrong results can both be measured and also calculated due to dynamic driving conditions such as strong acceleration, fast changes in steering angle, due to different quantities and distributions of the load, tire condition, tire air pressure, roadway conditions and its slope and lateral inclination, but also due to inaccurate mounting of the sensors. As a result, either the tolerance range for the mathematical value must be greatly increased, which prevents effective control, or the results of measurements and calculations must become more accurate, that is to say freed of distorting influences.
The invention therefore has the object of specifying a method which takes into consideration and eliminates all above possibilities of distortion in the measurement and mathematical value and in this manner provides the possibility of obtaining an accurately operating propulsion control system.
The invention also has the object of creating an arrangement or device for carrying out this method.
According to the invention, this object is achieved by providing a method wherein controlling propulsion in motor vehicles in the sense of maintaining stable driving conditions, in which method a variable characterizing the steady-state driving condition is measured and a mathematical value which adequately represents this variable is calculated by means of the vehicle speed and the steering angle, and in which method measurement value and mathematical value are compared with one another and control signals for the brakes and/or for a power actuator of the vehicle engine are generated in accordance with the result of the comparison, characterized in that the mathematical value (R.sub.R) is phase-delayed in dependence on at least one measurement variable (v) related to the dynamics of vehicle movement, that the difference between the phase-delayed mathematical value (R.sub.R) and the measurement value (M) is subjected to an averaging over a predeterminable period and this averaged value is added to the phase-delayed mathematical value and that the mathematical value (R.sub.S) corrected in this manner is compared with the measurement value, and that the difference (D) between the differences, produced in a particular time interval, of successive measurement values and phase-delayed mathematical values is formed and a particular parameter (EG) for calculating the mathematical value (R.sub.R) is changed in accordance with the value of this difference. According to this method, the invention is based on a multiple evaluation of the difference between measurement value and mathematical value and on a subsequent influencing of the mathematical value or at least of a parameter of the mathematical formula used. Instead of influencing the mathematical value, influencing the measurement value for reducing the difference is also within the scope of the invention even if this possibility is not expressly described.
The method according to the invention is used in a device according to the invention which comprises an arrangement for carrying out the method referred to above, comprising sensors for determining the vehicle speed, the steering angle and a measurement value for a variable characterizing the steady-state driving condition, particularly the lateral vehicle acceleration, the yaw velocity or the speed difference of the steered wheels of one axle associated with the steering angle, comprising adaptation electronics for adjusting the sensors, comprising a computing unit for calculating a mathematical value which adequately corresponds to the measurement value and is associated with the vehicle speed and the steering angle or a tolerance range around this mathematical value by means of a predetermined mathematical formula, and comprising a comparison unit in which the measurement value is compared with the mathematical value or its tolerance range and the output signals of which are control signals for the brakes and/or for a power actuator of the vehicle engine, characterized in that an electric filter (F) is provided, the filter parameters of which (A, B, C, D) can be predetermined in dependence on at least the vehicle speed (v) and which can be supplied with the output signal (R.sub.R of the computing unit (R), that a first correction unit (S) is provided which is supplied with the output signal (R.sub.F) of the filter (F) and the measurement value (M) as input variables and which forms the difference between those two values, subjects this difference to an averaging over a predetermined period and adds the result to the output signal (RF) of the filter (F), and that the mathematical value (Rs) corrected in this manner, together with the measurement value (M), are supplied as input variables to the comparison unit (K);
and that a second correction unit (L) is provided which is supplied with the output signal (R.sub.F) of the filter (F) and the measurement value (M) as input variables and which forms the difference .DELTA.M-.DELTA.R.sub.F) between the differences (.DELTA.M;.DELTA.R.sub.F), produced in a certain time interval (.DELTA.t) of successive measurement values (M.sub.1 ; M.sub.2) and filer output signals (R.sub.F1 ; R.sub.F2),
that a particular parameter (EG) of the mathematical formula used in the computing unit (R) can be changed in accordance with this difference (.DELTA.M-.DELTA.R).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.